Aircraft maintenance checks are periodic inspections that have to be done on all commercial/civil
aircraft after a certain amount of time or usage; military aircraft normally follow specific
maintenance programmes which may or may not be similar to those of commercial/civil operators.
Airlines and other commercial operators of large or turbine-powered aircraft follow a
continuous inspection program approved by the Federal Aviation Administration in the
United States, or by other airworthiness authorities such as Transport Canada or the European Aviation
Safety Agency.
Under FAA oversight, each operator prepares a Continuous Airworthiness Maintenance Program
under its Operations Specifications or "OpSpecs".
The CAMP includes both routine and detailed inspections.
Airlines and airworthiness authorities casually refer to the detailed inspections as "checks",
commonly one of the following: A check, B check, C check, or D check.
A and B checks are lighter checks, while C and D are considered heavier checks.
A Check This is performed approximately every 500
- 800 flight hours or 200 - 400 cycles.
It needs about 20 - 50 man-hours and is usually performed overnight at an airport gate or
hangar.
The actual occurrence of this check varies by aircraft type, the cycle count, or the
number of hours flown since the last check.
The occurrence can be delayed by the airline if certain predetermined conditions are met.
B Check This is performed approximately every 4–6
months.
It needs about 150 man-hours and is usually performed within 1–3 days at an airport
hangar.
A similar occurrence schedule applies to the B check as to the A check.
B checks may be incorporated into successive A checks, i.e.: A-1 through A-10 complete
all the B check items.
C Check This is performed approximately every 20–24
months or a specific amount of actual flight hours or as defined by the manufacturer.
This maintenance check is much more extensive than a B Check, requiring a large majority
of the aircraft's components to be inspected.
This check puts the aircraft out of service and until it is completed, the aircraft must
not leave the maintenance site.
It also requires more space than A and B Checks—usually a hangar at a maintenance base.
The time needed to complete such a check is generally 1–2 weeks and the effort involved
can require up to 6000 man-hours.
The schedule of occurrence has many factors and components as has been described, and
thus varies by aircraft category and type.
D Check This is by far the most comprehensive and
demanding check for an airplane.
It is also known as a Heavy Maintenance Visit.
This check occurs approximately every 6 years.
It is a check that, more or less, takes the entire airplane apart for inspection and overhaul.
Also, if required, the paint may need to be completely removed for further inspection
on the fuselage metal skin.
Such a check can usually demand up to 50,000 man-hours and it can generally take up to
2 months to complete, depending on the aircraft and the number of technicians involved.
It also requires the most space of all maintenance checks, and as such must be performed at a
suitable maintenance base.
Given the elevated requirements of this check and the tremendous effort involved in it,
it is also by far the most expensive maintenance check of all, with total costs for a single
visit ending up well within the million-dollar range.
Because of the nature and the cost of such a check, most airlines — especially those
with a large fleet — have to plan D Checks for their aircraft years in advance.
Often, older aircraft being phased out of a particular airline's fleet are either stored
or scrapped upon reaching their next D Check, due to the high costs involved in it in comparison
to the aircraft's value.
On average, a commercial aircraft undergoes 2–3 D Checks before it is retired.
Many Maintenance, Repair and Overhaul shops state that it is virtually impossible to perform
a D Check profitably at a shop located within the United States.
As such, only a few of these shops offer D checks.
Maintenance Review Board Initial aircraft maintenance requirements
are proposed in a Maintenance Review Board report based on Air Transport Association
publication MSG-3.
Modern transport category airplanes with MSG-3 derived maintenance programs employ usage
parameters for each maintenance requirement such as flight hours, calendar time, or flight
cycles.
Maintenance intervals based on usage parameters allow more flexibility in scheduling the maintenance
program to optimize aircraft utilization and minimize aircraft downtime.
References
External links Description of a D-Check at Aerosphere
Air Transport Association Federal Aviation Administration
FAA Flight Standards Information Management System
Description of Checks in relation to the Airworthiness System on SKYbrary